Emp, it is easy enough for highschool kids these days to find the new chemicals the day they come out. Shit, they are on email lists getting product updates. I understand it takes time to push laws through, but its not like they are hopping on the new chemicals as soon as they come out and moving forward. Look how long it took them to ban MDPV (sold as bath salts), mephedrone (sold as plant food), and methylone. They literally have new ones every week with a slightly different chemical structure.
Unfortunately, I am not sure making them illegal will stop them from being sold as "Molly" at festivals or in general since these crappy drugs have cheap precursors and can be made way cheaper. However, it sure will make a lot of kids think twice about ordering an already illegal substance to their mom and dads house from a random foreign supplier. It won't stop it but, it will minimize the amount of this junk circulating. You are right though, they will still have a month or so to stock up even if they are banned quickly which is going to make this very hard for law makers.